An engine may include an engine knock control system to increase engine efficiency and reduce the possibility of engine degradation. The knock control system may include a knock sensor that senses vibrations of the engine's block. The knock control system may observe particular frequencies output from the knock sensor to determine the presence or absence of engine knock. Engine knock or detonation may occur when end gases within the cylinder ignite before a flame front generated by a spark ignites the end gases during a cycle of a cylinder. The ignition of the end gases due to higher cylinder temperatures and pressures may stimulate vibration within the engine's block, which may be detected via the knock sensor. The knock system may determine that engine knock is present based on output of the knock sensor during a crankshaft interval where knock may be expected and an engine knock background noise level. The engine knock background noise level may reflect engine vibration when engine knock is not present. However, if the knock sensor degrades or if engine knock background noise level changes or varies from engine to engine, engine knock may not be observed by the control system or it may be falsely indicated by the control system. Therefore, it may be desirable to provide a way of operating the knock control system such that the possibility of missing knock or falsely indicating knock may be reduced.
The inventors herein have developed an engine operating method, comprising: sampling a first knock sensor in a knock window of a selected cylinder via a controller; and sampling a second knock sensor in the knock window of the selected cylinder via the controller in response to generating less than a threshold number of knock indications being generated from sampling of the first knock sensor in the knock window of the selected cylinder.
By sampling output of a second knock sensor in response to generating less than a threshold actual total number of engine knock indications being generated from sampling output of the first knock sensor, it may be possible to provide the technical result of improving engine knock detection during conditions where a knock sensor is degraded. Although the second knock sensor may not provide as desirable a signal to noise ratio as the first sensor with regard to detecting knock in a particular engine cylinder, it may provide a signal that is sufficient for detecting knock in the particular engine cylinder. The engine knock background noise level for the particular cylinder may be reassessed according to output of the second knock sensor. Additionally, the approach provides for adjusting fuel injector and poppet valve opening and closing times to provide additional ways to modify engine background noise levels so that engine knock detection may be improved.
The present description may provide several advantages. In particular, the approach may improve detection of engine knock. Further, the approach provides for increasing opportunities to learn engine knock background noise levels so that indications of engine knock may be more accurate. Further still, the approach may provide ways of changing engine knock background noise levels to improve signal to noise ratios for detecting engine knock.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.